Manufacture of lead sheet



March 20, 1956 RA|G ET AL I 2,738,572

MANUFACTURE OF LEAD SHEET Filed NOV. 1, 1951 2 Sheets-Sheet 1 nwz/vraqs' ROBERT (IPA/6 A, THO/14,46 THOMPSOA/ M W Wu r zw ATTam EV:

March 20, 1956 R. CRAIG ETAL 2,738,572

MANUFACTURE OF LEAD SHEET Filed Nov. 1, 1951 2 Sheets-Sheet 2 2,738,572 MANUFACTURE or LEAD snnnr Robert Craig, Heswall, and Thomas Thompson, Bromborongh, England, assignors to Unilever Limited, Port Sunlight, England, a British company Application November 1, 1951, Serial No. 254,244

Claims priority, application Great Britain November 9, 1950 7 Claims. (Cl. 29-4705) The present invention relates to lead sheet and tube and the manufacture thereof. a

Lead sheet is frequently used as a material for lining tanks in which acid reactions, for example, those involving the use of sulphuric acid, are carried out; When large panels are hung vertically, however, they tend to buckle and crack as a result of distortion due to changes in temperature and creep under the stress imposed by the weight of the material itself. It has already been proposedto fit hanging strips or lugs by means of which the sheet may be supported at a number of points. This, however, only partially overcomes the disadvantages of distortion. The disadvantages of lead tube are that it can only withstand limited pressures, and can only span a short distance without supports, owing to its lack of rigidity.

According to the present invention, lead sheet or tube has incorporated therein, a reinforcing mesh structure of a strain-resisting metal, for example, steel.

The mesh structure may comprise a net or fabric woven from wires of the strain-resisting material, or may con-.

sist of perforated sheets of such metal.

For reinforcing lead sheet, "expanded metal has been found particularly suitable because in the process of manufacture the ribs or strands of the expanded metal are twisted so that the plane of the rib lies at an angle to the plane of the sheet or expanded metal as a whole. This has the effect of increasing the overall thickness 'of the expanded metal, usually by three times its'thickness before expanding, thus providing a correspondingly greater degree of support for the lead sheet than would be the case if the ribs were not twisted.

The mesh structure may be incorporated into the lead sheet in any suitable way, for example by pressing, casting and like method. One suitable process, especially applicable to an expanded metal reinforcement has been found to be a method of rolling and in particular rolling combined heating. When heating is utilized, then owing to the fact that solid lead changes instantaneously to the liquid state without the. intervening plastic state encounteredin the caseof most other metals, it has been found important to heat the lead sheet so that its surface is liquefied only to a depth sufficient to ensure that thereinforcing mesh is embedded in the liquid. To do this, the surface of the lead sheet into which the reinforcement is embedded by rolling, is heated to liquefaction point immediately prior to rolling and the other surface is kept cool by rolling with a chilled roll.

To ensure adherence between the reinforcement and the lead surface, the surfaces of the lead and reinforcement which are contacted during rolling must previously have been tinned.

Therefore, in carrying out the process of rolling combined with heating a tinned surface of a lead sheet is heated to liquefaction and then passed with its liquefied surface in contact with a tinned surface of a sheet of reinforcing mesh through a pair of rolls, at least one of which is chilled, in such a manner that its 'solid surface is in contact with a chilled roll. v The terms tinned and tinningas used in this specification, refer to the application to the appropriate surfaces of the metal tin or of a tin alloy.

In carrying out the process, it is preferred to liquefy the tinned surfaceof the lead sheet to a depth which is sufficient to ensure that the reinforcing mesh sheetis embedded in lead throughout its entire thicknessto' obtain the most satisfactory bonding between the lead'sheet and the reinforcement.

The above process may be used to reinforce a single lead sheet oh one surface only. 'Alternatively, a sandwich maybe formed consisting of two lead sheets enclosing a single expanded metal sheet. To this end one tinned surface of each of the two lead sheets is liquefied, and the two sheets passed with the liquefied surfaces enclosing and in contact with a sheet of reinforcing mesh such as expanded metal tinned on both surfaces through a pair of chilled rolls with the solid surface of each lead sheet in contact with a chilled roll.

The invention will now' be described with reference to the accompanying diagrammatic drawings in which:

Fig. 1 is' a 'side view of apparatus for reinforcing two lead sheets with a single sheet of expanded metal, and

Fig. 2 is an end view of the apparatus of Fig. 1 looking in the direction of arrow X in Fig. l. v Referring to the drawings, rolls 1 and 2 are positively driven at the same speed by a variable speed; motor (not shown) capable of giving roll speeds from between 2 and 10 revolutions per minute. The roll 2 is provided with screws (notshown) for adjusting the gap between the rolls; 'A guide plate 3 is fitted below the'rolls, as

sliowmto direetLth'e material emerging from the rolls to onc's'ide 'thereof. The rolls are cooled internally by brine which enters"throughconduits 4 and 4 (Fig. l). and emerges from conduit 5 of roll 2' (Fig; 2) and a'cori'espondingi'conduit of roll 1 not shown). The brine is fed fronia coil immersed a tank '(not shown) containing industrial spirit which ,has been c'ooled'to -l0"; C; by the addition of solid carbon dioxide. i The rolls 1 and 2 are bridged by a steel frame which supports two roller conveyors 7 and 8 at a level such that lead s heetsfl and 10 carried by these roller conveyors respectively are tangential to rolls 1 and 2 respec tively. The frame 6 supports an upper frame 11 carry- 20 from which gas-fired radiant'heaters 21 and 22 are suspended by four screws 19a and 2011 respectively. The support plates are supported in this lowermost position by landings 19b and 20b on the frame 6 as in Figs 1 and 2. The heaters have heating surfaces of porous tile and are provided with control valves, gas governors and mixing chambers into.which compressed air which has previously been cleaned can be passed. The gas and compressed air conduits are shown as 23, 23 and 24, 24 respectively in Fig. 1. Large movements of the burners 21 and22 can be brought about by adjusting the positions'of the counterpoise weights 15 and 16. Fine adjustments'inthe positions'of the burners can be made by means of the screws 19a and 20a after the support plates 19 and 20 have dropped on to the landings 19b and20b respectively. I

The upper frame 11 also carries two vertical guide bars 25 and 26 (Fig. 2) of channel section between which the expanded metal sheet 27 is directed into the nip of the rolls 1 and 2.

3 operation of the above described apparatus is as ellew Two sheets of 8 lb. lead were prepared for tinning by wire brushing and scraping one surface of each until they w r b gh a free fro d scon inuities. These surfaces were immediately coated with a solder paint conta ni fine y p de ed s lder and an active rliquid flux to mi imi x d tion- ?Ehese she t w re then placed one on each of the conveyors 7 and 8 with the t nn d u a upp The reinforcing expanded metal sheet 27 consisted of a mesh, marketed in the already tinned state and which therefore required no prior treatment other than yigorous wash n and drying or being lo t d in the s d bars and 26.

.One end of each lead sheet was bent over its respeci e r ll and t e p n o t e shee on a eo y was -.adjustcd to be parallel to the side guides .on each conveyor. The end of each sheet was then placed in the nip of the rolls and compressed together for a few inches of their lengths by operating the rolls for a short time. Any solder paint removed during this handling was restored. The radiant heaters were arranged at a distance of about 18 inches above each sheet and insulating boards were placed between the heaters and the sheets. Chilled brine at --10 C. was circulated through the rolls until their temperature was reduced to -3 C. The radiant heaters were operated and adjusted to a uniform temperature of 840 C., which temperature was recorded by viewing the heaters with a disappearing filament type pyrom eter and then the insulating boards were removed. Both heaters were lowered simultaneously to within about /2 inch of the tinned surface of each sheet. The rolls were then operated again and as they began to rotate, the reinforcement was lowered in the nip between the two lead sheets.

The speed of the rolls was adjusted by manual con- ,trol of the variable speed motor so that :the time of travel of each sheet under the heaters was long enough to boil off the flux solution in the solder paint, thus removing the oxide film. At the end of its travel under the heater, the upper surface of each lead sheet was liquefied to a depth just suflicient to take half the thickness of the expanded metal without deforming its flanges. The reinforcement became embedded under the pressure of the rolls as the three sheets passed through the nip thereof. The reinforced sheet emerging from the nip of the rolls was guided to one side of the rolls .by the guide plate 3, and was allowed to cool to room temperature in thehorizontal plane.

Lead tube may be reinforced according to the invent-ion in the following way.

Two lead strips whose upper faces have been cleaned and coated with a suitable flux are each fed into a pair of forming rolls which convert the strips into half round sections. These sections, inclined at an angle of approximately 60 to one another, are then fed by pairs of feeding rolls, which maintain the sfimi circular form towards a pair of cladding rolls. Bisecting this angle, a single lead tube, wrapped externally with steel reinforcing wire having a tinned or soldered surface is fed vertically nt the n p o th rolls o her wit the two ha f und sections. As these sections converge towards. the junction they are preheated, for example by radiant heating elements, until, as they are about to pass through the rolls, the inner surfaces of the outer sections are almost fluid. In the nip of the rolls the combination of "heat and pressure results in the formation of a single tube of homogeneous structure.

The tube then passes to a further set of rolls whose function is to ensure the two open seams of the outer 1.3; sheath are filled and the two halves securely joined. These roll r o a a r g a g es t the cladding rolls and are provided with two electrically heated tubes which deposit molten lead into the two open seams before passing into the nip of the rolls, excess metal being removed from the roll by ascraper knife and finally from the tube by means of a die plate.

The invention is not limited to being carried out in the particular manner described. Many other ',ways of performing the invention will readily be apparent to those skilled in the art.

We claim:

1. A process of making reinforced lead sheet which comprises heating one tinned surface .of each of two lead sheets to liquefaction by radiant heaters operating at a temperature of about 840 C. and located about 0.5 inch from the tinned surface to be liquefied, passing the two sheets with the liquefied surfaces enclosing and in contact with asheet of expanded metal tinned .on'both sides through a pair of rolls chilled to about .--3 .C. in such a manner that the solid surface of each lead sheet is in contact with a chilled roll, the rolls being operated so that the time of travel of each lead sheet under the heaters is long enough to boil off any .fiux solution on the tinned surface of each lead sheet.

2. A process of making reinforced lead :Sheet which comprises heating the tinned surface of .a lead sheet .to liquefaction, contacting the liquefied tinned surface faceto-face with the tinned surface of a sheet of reinforcing mesh structure of a strain-resisting metal, pressing the mesh structure into the liquefied surface and solidifying the liquefied surface, the tinned surface of the lead sheet 'being liquefied to a depth which is suflicient to ensure that the sheet of reinforcing mesh is ultimately embedded in the freshly solidified lead throughout the whole .of its thickness.

3. A process of making reinforced lead sheet as claimed in claim 2 in which the steps of contacting and pressing are carried out simultaneously by .rolling.

4. A process of making reinforced lead sheet as claimed in claim 2 in which the steps of contacting, pressing and solidifying are carried out simultaneously by rolling between rolls, at least one of which ,is chilled.

5. A process of making reinforced lead sheet which comprises the steps of heating a tinned surface of .each of two lead sheets, contacting :the tinned surfaces each face-to-face with a sheet of reinforcing mesh of a strainresisting metal tinned on both sides, pressing the mesh structure into the liquefied surfaces and solidifying the liquefied surfaces, the tinned surface .of each lead sheet being liquefied to a depth which is suflicient to ensure that the sheet of reinforcing mesh is ultimately embedded in the freshly solidified lead throughout the whole of .its thickness.

6. A process of making reinforced lead sheet as claimed in claim 5 in which the steps of contacting and pressing are carried out simultaneously by rolling.

7. A process of making reinforced lead sheet as claimed in claim 5 in which the steps (i Contacting, pressing andsolidifying are carried out simultaneously by rolling between chilled rolls.

References Cited in the file of this patent UNITED STATES PATENTS 664,438 Sargent Dec. '25, 1900 1,280,909 Wales Oct. ;8, 1918 1,956,464 Palm Apr. 24, "1934 2,290,554 Hack July 2-1, 39.42 2,338,091 Brennan Jan. 4, 1944 2,367,715 Chapman Jan. 23. 1945 

1. A PROCESS OF MAKING REINFORCED LEAD SHEET WHICH COMPRISES HEATING ONE TINNED SURFACE OF EACH OF TWO LEAD SHEETS TO LIQUEFACTION BY RADIANT HEATERS OPERATING AT A TEMPERATURE OF ABOUT 840* C. AND LOCATED ABOUT 0.5 INCH FROM THE TINNED SURFACE TO BE LIQUFIED, PASSING THE TWO SHEETS WITH THE LIQUEFIED SURFACES ENCLOSING AND IN CONTACT WITH A SHEET OF EXPANDED METAL TINNED ON BOTH SIDES THROUGH A PAIR OF ROLLS CHILLED TO ABOUT -3* C. IN SUCH A MANNER THAT THE SOLID SURFACE OF EACH LEAD SHEET IS IN CONTACT WITH A CHILLED ROLL, THE ROLLS BEING OPERATED SO THAT THE TIME OF TRAVEL OF EACH LEAD SHEET UNDER THE HEATERS IS LONG ENOUGH TO BOIL OFF ANY FLUX SOLUTION ON THE TINNED SURFACE OF EACH LEAD SHEET. 